Apart from a few exceptions, most polymer materials are combustible. It is therefore necessary to modify these polymer materials to make them fire-retardant for many applications such as the construction, furniture, vehicle or electronics industry. To satisfy corresponding regulations or standard tests, organohalogen or organcophorus compounds are added in large amounts as flameproofing agents to plastics (G. Gechta, H. Mxc3xcller, Plastics Additives Handbook, Hanser Publishers 1993, pp. 708-725).
Organohalogen compounds that are not toxic in themselves can release corrosive pyrolysis components that are hazards to health in the event of a fire. Consequently, there have been numerous attempts to replace these critically evaluated organic flameproofing agents with other organic flameproofing agents, like melamine, or inorganic flameproofing agents. Antimony oxide, red phosphorus, ammonium polyphosphate, and inorganic boron compounds have been used, among others, as flameproofing additives in polymer materials alone or in combination.
Hydroxides of di- and trivalent metals are being increasingly used as fully nontoxic and noncorrosive flameproofing agents. Aluminum and magnesium hydroxide have gained particular significance (G. Kirschbaum Kunststoffe 79, 1989, pp. 1205-1208 and R. Schmidt, Kunststoffe 88, 1998, pp. 2058-2061). Both hydroxides release water in the temperature range between 200-400xc2x0 C., which absorbs energy by evaporation and therefore leads to cooling of the polymer materials. The smoke density is also reduced.
The very high quality which is necessary in order to make polymer materials flameproof enough that they can pass fire tests is mentioned as a drawback of these hydroxide flameproofing agents. In addition, the extrusion and mechanical properties of these polymer materials, however, deteriorate to a high degree because of the high degree of filling.
Consequently, there has been several attempts to reduce the amount of these hydroxide flameproofing agents by combination with additional organic or inorganic flameproofing agents.
For example, JP 63 273,693-A, JP 63 030,588-A, JP 62 101,644-A as well as EP 333514-A describe flameproof polymer materials and coatings that contain metal hydroxides as flameproofing additives and clay minerals, like kaolin, mica, vermiculite or bentonite or montmorillonite as filler.
JP 55 112,248-A describes flameproof polyolefin materials for cable insulation that contain aluminum hydroxide, zinc borate, calcium carbonate, talc and bentonite in a particle size from 0.01 to 30 xcexcm.
JP 62 181,144 describes flameproof polyester, polypropylene and polyvinyl fluoride films that contain phosphorus-, nitrogen- or halogen-containing flameproofing agents and are coated with a mixture of layer silicates that are swellable in water, like montmorillonite, vermiculite or hectorite with silanes as coupling agent.
Attempts have also been made to improve flameproofing by addition of organically intercalated bentonites or montmorillonites. J. W. Gilmann and J. D. Lichtenhan (SAMPE Journal, Vol. 33, 1997, No. 4, pp. 40-46) describe so-called nanocomposites based on polyamide 6. These materials consist of a polyamide 6 matrix in which montmorillonite particles are dispersed that were intercalated beforehand with aminododecanoic acid. Addition of between 2 and 5% of this nanocomposite filler leads to a reduction of peak-of-heat release (PHR) by up to 63%.
Since adequate flameproofing cannot be guaranteed with organically intercalated layer silicate fillers as the only flame-retardant additives, attempts have also been described to combine organically intercalated clay minerals with other flameproofing agents.
EP 239 986-A describes a non-dripping, flameproof thermoplastic copolyester composition containing 5 to 35% of a flameproofing agent mixture. This mixture contains a bromine- or chlorine-containing compound with at least 50% Br or Cl, 0.2 to 1.5 parts by weight antimony oxide per part by weight of the bromine- and chlorine-containing compound, as well as at least one part by weight of a quaternized bentonite as an antidrip agent, 5 to 100 parts by weight aluminum hydroxide and up to 100 parts by weight calcium carbonate, each based on 100 parts by weight copolyester. Addition of aluminum hydroxide and calcium carbonate is supposed to reduce the smoke density and increase charring.
U.S. Pat. No. 5,773,502 describes a non-dripping, flameproof thermoplastic polyester material that contains the following flameproofing additives: 5 to 20 wt % halogen-containing organic flameproofing agent, 1 to 5 wt % antimony oxide, 0.25 to 5 wt % of an organophilic clay and 0.02 to 2 wt % of a fluorine-containing polymer.
GB-A 1 14 174 describes a polymer composition that contains 0.5 to 50 wt % of a flameproofing agent and up to 10 wt % of a bentonite modified with organic cations in addition to the base polymer (polyamide, polystyrene or polyolefin). Phosphoric acid esters, antimony trioxide or arsenic trioxide are used as flameproofing agents in addition to halogenated organic compounds. The use of magnesium, calcium or aluminum hydroxide as flameproofing agents is not described.
EP 132 228-A describes flame-resistant reinforced polyester molding compounds with 3 to 50 wt % reinforcing filler (preferably glass fibers), 5 to 30 wt % of a flame-resistant additive, 0.2 to 4 wt % of an optionally organically modified layer silicate as an antidrip agent and 0.05 to 2 wt % of an alkali metal salt of a monocarboxylic acid with 6 to 22 carbon atoms. Quaternized bentonites, like Bentone(copyright) 27, 34, 38 are preferably used as antidrip agents. Appropriate flameproofing additives are preferably organic halogen compounds alone or in combination with antimony trioxide. However, there is no indication of the use of hydroxides as flameproofing additives.
All the mixtures described above, including organically modified. Layer silicates and additional flameproofing additives have the common feature that these mixtures contain more or less toxic components and/or corrosive components in the event of a fire.
Flameproof halogen-free polymer compositions are known from EP 0 893 469-A that contain a mixture of different polymers or copolymers and an inorganic filler, like aluminum trihydrate or magnesium hydroxide.
It has now surprisingly been found that a synergistic flameproofing effect occurs for flameproofed polymer mixtures that contain essentially no additional organohalogen or organophosphorus flameproofing agents, if they contain in addition to metal hydroxides, organically intercalated layer silicates and optionally other inorganic flameproofing agents.
The object of the invention is therefore a flameproof, essentially halogen-free, polymer composition containing:
a) 100 parts by weight of a thermoplastic, crosslinkable or crosslinked elastomeric and/or thermosetting polymer;
b) 10 to 200 parts by weight magnesium, calcium, zinc and/or aluminum hydroxides and/or their double hydroxides;
c) 1 to 50 parts by weight of an organically intercalated layer silicate.
The layer spacing of the organically intercalated layer silicate in the polymer is preferably at least 10% greater than that of the original layer silicate.
The development objective was to prepare flameproof polymer compositions in which the use of organic halogen compounds and organic phosphorus compounds are dispensed with since such substances release toxic and/or corrosive gases in the event of fire.
xe2x80x9cEssentially halogen-freexe2x80x9d is understood according to the invention to mean polymer compositions whose halogen content (referring to low-molecular halogen compounds) is less than 5 wt %, preferably less than 2 wt %. If the polymers are halogen-containing polymers (for example, PVC), their halogen content is not considered here.
By omitting the organohalogen compounds, an improvement in the mechanical properties and charring is surprisingly achieved.
The effect according to the invention is probably based on the fact that the layer spacing determined by x-ray of the organically intercalated layer silicate is widened by the incorporation of the polymer molecules and that the organic halogen compounds are bound to the layer silicates so that they can no longer act as radical scavengers in the gas phase in the event of fire and the radical chain reactions that occur during combustion can run undisturbed. Use of an additional amount of the organically intercalated layer silicates without simultaneous use of an organohalogen compound causes a significant improvement in mechanical properties with comparable flameproofing properties, and also an improvement in charring.
The hydroxides or double hydroxides of magnesium, calcium, zinc and/or aluminum used according to the invention liberate water exclusively in the event of fire and therefore do not form toxic or corrosive smoke products. Moreover, these hydroxides are in a position to reduce the smoke density in the event of fire.
The employed polymer (a) according to the invention is preferably chosen from polyolefins (like polyethylenes, polypropylenes or polybutenes); vinyl polymers (like Polyvinyl chloride or polyvinylidene chloride); styrene polymers, polyacrylonitrile; polyacrylates and methacrylate; natural and synthetic rubbers; fluorine plastics (like tetrafluoroethylene or polyvinyl fluoride), thermoplastic polycondensates (like polyamide, polyesters, polycarbonates, polyethylene terephthalate); thermosetting polycondensates (like phenol-formaldehyde plastics, urea-formaldehyde plastics, melamine-formaldehyde plastics, unsaturated polyester resins, silicone resins, polyimide); thermosetting and thermoplastic polyadducts (like epoxy resins, polyurethanes and isocyanate resins); co- or terpolymers, as well as graft polymer from them; and their mixtures.
A summary of appropriate plastics can be found in Hans Domininghaus xe2x80x9cPlastics and their properties,xe2x80x9d second edition, VDI Verlag, pp. 7 to 11.
In order to achieve a flameproof finishing required for different applications, the percentage of hydroxide (b) is preferably about 30 to 80 wt %. At higher percentages of filling, the mechanical properties of the corresponding polymer materials deteriorate unacceptably. The tensile strength and breaking elongation, which is important for cable insulation in particular, also decline to an unacceptable degree.
However, it was surprisingly found that the amount of added flameproofing hydroxides (b) can be substantially reduced if organically intercalated layer silicates (c) are incorporated in the polymer mixtures as additional flameproofing additives. A synergistic effect is found between the organically intercalated layer silicate and the flameproofing hydroxides. For example, by addition of 5 wt % of the organically intercalated layer silicates, the aluminum hydroxide fraction can be reduced by 15% so that with improved flameproofing, higher breaking elongation and reduced processing viscosity occurs.
The metal hydroxides (b) preferably have a specific surface area of 3 to 150 m2/g, especially 3 to 50 m2/g and an average particle size of about 1 to 20 xcexcm, preferably about 1 to 10 xcexcm.
The metal hydroxides (b) can be modified on the surface, for example, hydrophobized, for example with silane.
Swellable smectites, like montmorillonite, hectorite, saponite or beidellite are preferably used as the starting materials for the organically intercalated layer silicates (c).
The organically intercalated layer silicates have a layer spacing of about 1.5 to 4 nm. These layer silicates are preferably intercalated with quaternary ammonium compounds, protonated amines, organic phosphonium ions and/or aminocarboxylic acids.
Preferably about 1 to 100 parts by weight of additional halogen-free flameproofing additives can also be added, like antimony oxide, red phosphorus, zinc sulfide, melamine derivatives, organophosphorus compounds and/or inorganic boron compounds.